The invention relates to a dispersive optical waveguide array.
Such arrays are known for use in multiplexers and demultiplexers and may comprise an array of optical waveguides of different pathlength thereby inducing phase changes between optical signals transmitted through the different waveguides within the array. Such systems may comprise a plurality of waveguides each arranged around a curved path so as to introduce different optical pathlengths. Such a system is for example shown in OPTICS LETTERS Jan. 1, 1995, volume 20, No 1.
Known systems of curved waveguides for a dispersive array may employ a plurality of curves of non-uniform radius of curvature. Such systems result in different physical pathlengths along the curve of each waveguide in the array. Furthermore the change of angle between the input and output end of each curved waveguide is not uniform for each of the waveguides in the array. These variations may cause unwanted signal variations between the light transmitted through the various waveguides in the array.
It is an object of the present invention to provide an improved waveguide array which reduces signal variations dependent on the particular waveguide within the array which is used to transmit the signal.
The invention provides a dispersive optical waveguide array comprising a plurality of optical paths of different optical pathlength arranged in parallel, which array includes a plurality of curved waveguide sections each of the curved sections having the same curvature and the same section length around the curve.
Preferably said curved sections are arranged so that optical axes of the inputs to the curved sections are all parallel to each other and the optical axes of the outputs of the curved sections are all parallel to each other.
Preferably input waveguide extensions are formed at the input end of the curved waveguide sections, the straight input waveguide extensions having different lengths from each other so that the input extensions have input ends aligned transverse to the optical input axes of the input waveguide extensions.
Preferably straight output waveguide extensions are formed at the output end of the curved waveguide sections, the straight output waveguide extensions having different lengths from each other so that the output extensions have output ends aligned transverse to the output optical axes of the output waveguide extensions.
Preferably a focussing element such as a curved mirror is provided to direct light into an input end of the array.
Preferably a focussing element such as a curved mirror is provided to direct light received from an output of the array.
The array may be integrated on a planar substrate.
The array may be formed as an integrated semiconductor chip.
The array may comprise a plurality of silicon on insulator waveguides.
The waveguides may be a plurality of ridge waveguides.
Preferably the waveguide array is formed as an integrated semiconductor chip and the or each mirror is formed by etching the semiconductor chip.
Preferably each mirror comprises a curved trench wall etched in the semiconductor.
The invention includes a dispersive optical waveguide array as aforesaid having at least one optical fibre connected to a waveguide coupled to one end of the array and a plurality of optical fibres connected respectively to a plurality of optical waveguides at the other end of the array.